Computational fluid dynamics assessment of the Helium-3 Enhanced Negative Reactivity Insertion (HENRI) system for the Transient REActor Test (TREAT) facility

Abstract

The Transient REActor Test facility (TREAT) is an air-cooled, graphite moderated nuclear reactor that is used for irradiation testing of nuclear fuels and materials. The shutdown of the Halden reactor in Norway lead to an increased interest of an indigenous nuclear facility that can perform Reactivity Initiated Accident (RIA) tests for Light Water Reactors (LWRs). Idaho National Laboratory (INL) has been leading the effort of making minor modifications to the TREAT facility to enhance its testing capabilities so it can mimic the neutronic boundary conditions representative of a RIA for a LWR. The power burst of the TREAT reactor needs to be shortened from 89 to 40 msec. to properly irradiate the fuel sample under RIA conditions. INL has proposed to use helium-3, a strong neutron absorber, as a form of negative reactivity to shorten the pulse of the reactor. In support of the development of a transient control rod for the TREAT, a Computational Fluid Dynamics (CFD) model is needed to confidently simulate the density evolution of helium-3 in this system.